GMC 2008 Yukon Denali Owner's Manual page 11

CAUTION:
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Sitting in a reclined position when your vehicle
is in motion can be dangerous. Even if you
buckle up, your safety belts cannot do their
job when you are reclined like this.
The shoulder belt cannot do its job. In a crash,
you could go into it, receiving neck or other
injuries.
The lap belt cannot do its job either. In a crash
the belt could go up over your abdomen. The
belt forces would be there, not at your pelvic
bones. This could cause serious internal
injuries.
For proper protection when the vehicle is in
motion, have the seatback upright. Then sit well
back in the seat and wear your safety belt
properly.
Do not have a seatback reclined if your vehicle is
moving.
Your vehicle has a memory function which allows seat
settings to be saved and recalled. See Memory Seat,
Mirrors, and Pedals on page 1-4.
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